OK the old 4.2 with 4.0 heads thing.

roundycorner · #1 (**permalink**) 03-07-2008, 10:45 PM

I need to replace/rebuild the 4.2 engine in my 90 yj.
I will probibly go with the mopar injection upgrade.
My real question is "do I rebuild my 253? do I build a 4.0 with the 4.2 crank and rods? or do I just use the 4.0 head on my 4.2? and if so what vintage is the best?
If I do the latter ,I know I will have to have some water ports welded or sealed so is it better to just buy a 4.0 head for it all ready done?
" As you can see I need some serious expert help here."
Thank you and make your weekend GREAT!
Quim

redrooster · #2 (**permalink**) 03-08-2008, 12:08 AM

I'm not familiar with the Mopar injection kit, but if you are going to get the 4.0 head, I would think that you could also get the intake, throttle body, sensors and all from a salvage yard. You could probably get a whole 4.0 for less than the cost of the Mopar kit. You may still want to get a Mopar or Painless harness. Seems like you could save some big money that way.

Bounty__Hunter · #3 (**permalink**) 03-08-2008, 10:00 AM

For the 4.6L stroker, pick up a 4.0L engine and drop in the 4.2L crank. There's a little more to it, so you may want to google 'jeep stroker' or '4.0 stroker'.

Or you could put the 4.0L head on your 4.2L ( 258 ) engine. The intake will mount up a little higher, so there's some slight modification, but nothing serious. Plenty of web writeups on that too, try googling '4.0 head swap' or '4.2 head swap' or 'jeep head swap'.